1. Field of the Invention
The present invention relates generally to computer aided design (CAD) applications, and in particular, to a method, apparatus, and article of manufacture for enabling, in a building information model (BIM) CAD application, direct manipulation techniques that allow walking a composable model and modifying the model with intuitive user interaction in two-dimensions (2D) as well as three-dimensions (3D).
2. Description of the Related Art
Grading is configuring the land's surface by removing or adding soil and other earthen material to artificially shape the land to best suit a project. The grading of a site serves three basic purposes: functional, drainage, and aesthetic. These basic purposes often conflict with each other and prior art solutions fail to provide an easy mechanism to satisfy all of these purposes while utilizing a single grading model as the user proceeds from concept to completion of a project. Such problems may be better understood with a description of prior art grading and grading solutions.
Functionality: Terrain grading is used to re-form terrain/land in order to provide land that is functional or can be used for a functional purpose. In this regard, grading reforms the terrain to make it compatible for an intended land use. Such functional land uses may include parking lots, ponds, swales, and other features. To provide for such land use, terrain grading creates finish smooth slopes at specified grades.
Facilitate Drainage: Grading establishes and controls the new drainage pattern to direct the runoff to outfall points and away from buildings.
Aesthetic: A good design creates an aesthetically pleasing and appealing landscape. Natural landforms are created by using concave and convex shaped slopes rather than uniform gradient slopes. The creation of aesthetic landforms must be balanced by the cost of constructing them.
These goals often conflict with each other and to integrate them into the final design, they must be analyzed collectively. In practice, a grading plan is established through several successive trials of different schemes. This process can be very tedious. A grading scheme often involves projecting slopes from curves representing shoulder edges or water boundaries, and leveling them against the existing terrain. The implementation of this concept is fraught with difficulties due to a variety of complex scenarios that could not be handled by a naïve ray projection algorithm, especially when projecting from curves with rapid elevation changes.
More specifically, prior art products provide a grading scheme by projecting each segment of a curve at a given cross-slope to produce bounded panels, and then combining them. Such a methodology involves complex models whose history of operations is difficult to track. The complexity of the existing solution results in difficult (if not impossible) software implementations that are error prone, unstable, and may completely fail (if supplied geometry is complicated). Accordingly, users are hesitant to use the prior art product on account of such stability problems. The prior art also provides few tools to modify existing solutions in an intuitive manner. Further, the prior art fails to provide tools that can be used in a conceptual design that can also later be refined for generating production drawings. In this regard, it is desirable to provide a tool that can be used to obtain quick answers for early decision making (e.g., approximate values of earthwork quantities) that can be refined later to produce a more accurate solution.
As described above, a particular need is that of designing the terrain to facilitate drainage. The prior art provides a complex methodology that is neither natural nor user friendly. In this regard, the prior art measures the cross grade (or cross slope) perpendicular to the curve from which a slope is projected. Each segment of the curve is projected at a given cross-slope to produce bounded panels that are combined by intersecting them against each other. This approach involves complex algorithms to solve inside corners and the intersection of overlapping solutions. For example, the rapid transitions of offsets across the inside corners cause incomplete or failed 3D intersections of the adjacent, bounded planes. Likewise, a multi-elevation rounded corner projected beyond its radius produces equally complex intersection geometry. The intersections are solved by simplifying the geometry and integrating the solution into planar topology to remove redundant loops. However, stability problems and specialized functionality restrict the use of the prior art methods.
Thus, prior art solutions produce inside corners with complex geometry that is hard to clean, especially if the solutions involve degenerate partial solutions. Solving such inside corners involves complex algorithms and is a cumbersome process. In addition, when designing the drainage, the prior art fails to provide the ability to create or use organic shapes that could be used to produce an aesthetically pleasing landscape.
Moreover, there are few tools for modifying prior art solutions in ways that directly map to site development needs. Even though there is a large set of elevation/grade editing tools, the overlapping line work can create difficult to resolve stability problems and elevation conflicts. Predicting the impact of an edit to a solution requires experience, and factors like tessellation quality, crossing break lines, and Delaunay triangulation rules can confound a new user.
Accordingly, while prior art solutions may provide a model for visualizing and grading a terrain, such prior art models have various limitations. For example, in prior art solutions, the history of the model cannot be viewed interactively, users cannot track the order of operations, and consequently, users may not be provided with the ability to understand how a model was built. Such a lack of understanding gives rise to a communication gap across engineers working on the same project. In addition, existing prior art models do not allow the user to click the model elements and modify them interactively in 3D. Also, prior art models fail to provide a mechanism for modifying offsets and slopes interactively.
As described above, the existing solution does not allow the creation of a conceptual model that can later be refined into a more accurate model. In practice, before any detailed grading plans are underway, the designer needs to develop a generalized grading scheme to determine any problem areas and get a feel for the type of limitations the site may have as the design progresses. In the preliminary analysis, engineers are often looking for quick early-stage approximate answers (like road and parking area gradients, drainage patterns, rough estimates of cut and fill quantities, need for steep slopes, retaining walls, etc.) to make quick decisions that can later be refined into more accurate solutions for production drawings. The prior art fails to provide such capabilities.
In view of the above, it is desirable to enable a single set of tools that can be used from concept through completion, in the same environment, while allowing the user to design a grading solution in a natural, interactive, direct, and desirable manner.